Transformer

ABSTRACT

A transformer having primary and secondary windings on a conductive non-magnetic bobbin. A pot-type core surrounds the bobbin and windings and has a central magnetic core extending axially into the bobbin and windings. Flanges on the bobbin separate the primary from the secondary, and the flanges and bobbin have a slot to limit induction current losses. The secondary is center-tapped, and the flanges and conductive, nonmagnetic outer case prevent electric field coupling and suppress leakage at the center tap.

United States Patent [1 1 Kubota'et al.

[ 1 TRANSFORMER 51 Feb. 20, 1973 3,517,361 6/1970 Reifel et al. ..336/84 [75] Inventors: Yasuharu Kubota, Fujisawas hi, izgi'ggg 1/132: Young 33:23:18;

Kanagawa ken Susumu Agawa I ayne Kamakura shi Kanasawa ken be; 2,183,355 12/1939 Mavener ..336/84 7 of Japan 1 FOREIGN PATENTS 0R APPLICATIONS [73] A'ssignee: Sony Corp., Tokyo, Japan 733,913 4/1943 Germany ..336/84 I22] Filed: 1971 Primary Examiner -Thomas J. Kozma [21] Appl. No.: 173,979 Attorney-Lewis I-I. Eslinger et al.

[30] Foreign Application Priority Data [57] ABSTRACT A transformer having primary and secondary windings Aug. 22, 1970 Japan ..45/83785 on a conductive nommagnetic bobbin. A p yp I core surrounds the bobbin and windings and has a '8" 4 a: central magnetic core extending axially into the bob. bin and windings. Flanges on the bobbin separate the I [58] Field of Search ..33,6/69, 70, 84, 83 p y from the secondary, and the flanges and bob [56] References Cited bin have a slot to limit induction current losses. The I v secondary is center-tapped, and the flanges and con- UNITED STATES PATENTS ductive, non-magnetic outer case prevent electric field 2 896096 1/1959 Schwarzer ..336/84 x coupling and suppress leakage the center 2,085,434 6/1937 Loftis et al ..336/84 x 2 Chin, 19 Dmfl'ngngum 2,533,920 12/1950 fCrook ..'.....336/84X H i I l I Pmmmm mam/1 y INVENTORS YASUHARU KUBOTA' SUSUMU TACAWA LEWIS H. ESLINGBR ATTORNEY V I I PAINTED-F5820 m3 sum 3 or 4 S3 =SCIL+ S I.

' YINVENTORS HARU KUBOTA susunu TAGAWA LEWIS n. ESLINGER ATTORNEY TRANSFORMER BACKGROUND OF THE INVENTION 1. Field of the Invention This relates to the field of transformers for coupling video.signals and particularly to means for shielding primary and secondary windings to prevent undesired electric field coupling therebetween.

2. Prior Art A pickup tube of the type having a target with a multiplicity of color filters and signal plates extending transversely of the direction of line scan has been disclosed in U.S. Pat. No. 2,446,249. In this type of pickup tube the signal plates corresponding to the color filters are connected to bus bars and the respective primary color video signals are derived from three signal output terminals connected to the bus bars. However, this pickup tube is defective in that each primary color video signal is mixed with other primary color video signals due to the electrostatic capacity coupling present between the respective signal electrodes. This results in crosstalk which lowers the color purity of the 7 color video signal.

There has been proposed a system such as disclosed in U.S. Pat. No. 3,502,799 in which a plurality of index signal images and striped color component images are optically formed on the target of a vidicon tube to produce a composite color-video signal with an index. With this system, however, the ratio between the color component image area and the effective scanning area of the vidicon is decreased by an amount correspond- -ing to the index signal images. This results in lower resolution. Further, this prior art system necessitates a complicated and expensive device for optically forming the index signal images on the target.

' In U.S. application Ser. No. 72,593 entitled COLOR TELEVISION CAMERA and filed Sept. 16, 1970 in the name of Yasuharu Kubota, one of the inventors of the present case, there is described an improved color television pickup tube and system. The pickup tube described in that application has a plurality of electrodes, a color filter and a photoconductive surface and is adapted to form color separated images on the photoconductive layer. In addition, an alternating volt-' age is supplied to the plurality of electrodes. Accordingly, a predetermined pattern of potential changes is formed on the surface of the photoconductive layer of thepickup tube which is reproduced as an index signal. In this manner the index signal does not narrow the dynamic range of the image pickup tube and the resolution of the color video signal is not lowered. i

The index signal, luminance signal and chrominance signal are not derived from each electrode but are picked up in the form of one composite signal, so that even if crosstalk exists between the electrodes, color difference signals can be readily derived from a demodulator circuit, and accordingly a color video signal of good white balance can be obtained.

Since the index signal is obtained at the output of the pickup tube by supplying an alternating voltage to the electrodes in synchronism with the line scanning period of the pickup tube, demodulation of the color video signal is easily accomplished. Further, when the color video signal is reproduced without the chrominance signal, the index signal is simply obtained by adding to the output of the image pickup a signal produced by delaying the pickup tube output by one horizontal scanning period. In this manner, there is no possibility of the index signal being mixed with the demodulated color video signal.

In the device of application Ser. No. 72,593, supra, the index signal and the chrominance signal are in the same band, and hence the bands of the luminance signal and the chrominance signal can be widened to thereby a color video signal with high resolution. In addition, since the index signal and the chrominance signal are derived from a common preamplifier and filter, no difference in the delay time between these signals is produced and, accordingly, a picture of excellent white balance can be obtained. Further, the index signal does not interfere with the chrominance signal, and hence the picture quality is not degraded.

The formation of the color separated images on the photoconductive layer of the pickup tube may be accomplished by any conventional method. For example, a lens screen consisting of many lenticular lenses can be disposed on the surface of the face plate of the pickup tube and the image of a color filter consisting of a plurality of pairs of striped color filter elements and interposed between an object to be televised and the lens screen is projected by the lens screen onto the photoconductive layer and, at the same time, the image of the object being televised is caused by an objective lens to overlap on the image of the color filter. Further, it is also possible that the image of the object to be televised is focused by an objective lens onto the In the pickup tube employed in this invention its rela-.

tive position to the color filter need not be adjusted with high accuracy, and hence adjustment of the pickup tube is easily accomplished.

It has been found that the transformer used for supplying index signals to the electrodes in the pickup tube in U.S. application Ser. No. 72,593, supra, may have undesirable leakage between the primary and secondary. Such leakage may cause unbalanced index signals and a deterioration of color fidelity, for example, by producing a pattern of bright and dark lines in the reproduced television picture.

Accordingly, it is a principle object of the present invention to provide an improved transformer having reduced leakage current.

A further object is to provide a transformer having a reduced leakage and capable of handling low level video signals from a television pickup tube.

Further objects will be apparent from the following I specification together with the drawings.

BRIEF DESCRIPTION OF THE INVENTION on it is enclosed in a non-magnetic, conductive shield, and the shield, the flanges, and the bobbin all have slits to prevent losses due to induction currents. Connections to the primary winding are enclosed in a conductive, braided wire shield connected to the outer case.

The wire leads of the secondary winding extend from the conductive shield case and are twisted together to equalize capacitance between these leads and ground. The other ends of the winding are joined together to form the center tap of the secondary winding, and the wire sections adjacent the center tape are twisted together so as to also have equal capacitances to ground. The entire conductive shield case with the bobbin and windings therein is enclosed within a suitable magnetic pot-type core that has a central projection that extends into the hollow bobbin and has an outer portion that completely encloses the transformer except for openings to permit the leads to pass through.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram illustrating one example of a color television camera incorporating the transformer of the present invention.

FIG. 2 is a perspective view partly in cross-section showing the principle parts of the pickup tube employed in the camera of FIG. 1.

FIGS. 3 and 4 are waveform diagrams for explaining the operation of the camera in FIGS. 1 and 2.

FIG. 5 is a graph showing one example of a frequency spectrum for a color video signal produced by the color television camera shown in FIGS. 1 and 2.

FIG. 6 is an end view of a transformer constructed according to the invention and with parts broken away to show some of the interior construction.

FIG. 7 shows the bobbin used in the transformer of FIG. 6.

' FIG. 8 shows the outer shield case to be used with the bobbin in FIG. 7 in manufacturing the transformer of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION In order to provide a suitable background for explanation of the present invention, a color video camera in which the transformer of the present invention may be used will first be described. FIG. 1 illustrates the fundamental concepts of this invention. In FIGS. 1 and 2, two sets of electrodes A (A,, A A,, A,) and B (B,, B B,, B,,) are disposed adjacent the photoconductive layer 1 of a pickup tube 2. The photoconductive layer 1 is formed, for example, of materials such as antimony trisulfide, lead oxide, etc. The electrodes A and B are transparent conductive layers formed of tin oxide including antimony and they are alternately arranged in an order which may, for example, be A,,B,,A,,B,, A,,B,, A,,,B,,, the electrodes being respectively connected to terminals T and T, for connection with external circuits. In this case, the electrodes are disposed so that their longitudinal directions may cross the horizontal scanning direction of an electron beam.

The electrodes A and B are disposed on one side of a glass plate 3, on the other side of which an optical filter F made up of red, green, and blue color filter elements F,,, F,; and F, arranged in a repeating cyclic order of F,, F,;, F,,, F,,, F,,, F,,, are disposed parallel to the length of the electrodes A and B in such a manner that each triad of red, green, and blue color filter elements F F and F may be opposite to each pair of adjacent electrodes A, and 13,. So long as the electrodes A and B and the optical filter F are aligned with each other in their longitudinal directions, their relative arrangement is optional. The optical filter F is fixed to the faceplate 4.

The pickup tube 2 has enclosed therein the photoconductive layer 1, the electrodes A and B, the

glass plate 3, the optical filter F, and the faceplate 4 mounted on one side of the tube envelope 5. About the image tube 2 there are mounted a deflection coil 6, a focusing coil 7, and an alignment coil 8. Reference numeral 9 indicates an imagelens, by means of which the image of an object 10 to be televised is focused on to the photoconductive layer 1 through the faceplate 4. Reference numeral 11 designates an electron gun for emitting an electron beam.

The operating circuit for the tube 2 includes a transformer 12 that consists of a primary winding 12a and a secondary winding 12b having a mid tap t The terminals t, and t, of the secondary winding 12b are respectively connected to the terminals T, and T of the image pickup tube 2. The primary winding 12a is connected to a signal source 13 which produces an alternating signal 8,, shown in FIG. 3, that is synchronized with the line scanning period of the image pickup tube 2. This alternating signal S, has a rectangular waveform with a pulse width equal to a horizontal scanning period II of the electron beam, namely a pulse width of, for example, 63.5 microseconds and a frequency of 7.875 KHz, which is one-half of the horizontal scanning frequency. The midpoint t of the secondary winding 12b of the transformer 12 is connected to the input of a preamplifier 15 through a capacitor 14 and is supplied with a DC bias voltage of 10 to 50V from a power source B+ through a resistor With such an arrangement, the electrodes A and B are alternately supplied with voltages higher and lower than the DC bias voltage for every horizontal scanning period, so that a striped potential pattern corresponding to the electrodes A and B is formed on the surface of the photoconductive layer 1. Accordingly, when the image pickup tube 2 is not exposed to light, a signal S, corresponding to the rectangular waveform illustrated in FIG. 4A is derived at the midpoint t, of the secondary winding 12b in a scanning period I-I, due to electron beam scanning. When a DC bias voltage of, for example, 30V is supplied to the midpoint t, of the secondary winding 12b and an alternating voltage of 0.5V is impressed between the terminal T, and T,,, a current flowing across the resistor R varies by 0.05 microamperes, which can be used as an index signal. The frequency of this index signal S, is optionally determined with reference to the width and interval of the electrodes A and B and one horizontal scanning period of the electron beam, and can for example be 3.58 MHz. When the image of the object 10 is focused on the photoconductive layer 1, signals corresponding to the light intensity of the filtered red, green, and blue components are produced on the photoconductive layer 1 in overlapping relation with the index signal S, to produce a composite signal S, such as illustrated in FIG. 4B, in which the reference characters R, G, and B respectively designate portions of the composite signal 8, corresponding to the red, green, and blue color components. The composite signal S, is the sum of the luminance signal Sy, the chrominance signal S and the index signal 5,, namely S, =S +S +S,. The frequency spectrum of the composite signal 8,, as illustrated in FIG. 5, is determined by the width of the electrodes A and B, the width of the optical filter F, and the horizontal scanning period. That is, the composite signal S, in its entirety is in a bandwidth of 6 MHz and the luminance and chrominance signals S, and S are respectively arranged in the lower and higher bands. It is preferred to minimize overlapping of the luminance and chrominance signals S, and S and, if desired, it is possible to dispose a lenticular lens or the like in front of the image pickup tube 2. This optically lowers resolution and narrows the luminance signal band.

In the next horizontal scanning period H the voltage (the alternating signal) applied to the electrodes A and B is reversed in phase, in which case an index S, is produced such as depicted in FIG. 4A which is opposite in phase to the index signal S, shown in FIG. 4A. Accordingly, a composite signal S, is derived at the input side of the preamplifier as shown in FIG. 4B, namely S,'=S l'-S -S,.

Such a composite signal S, (or 5,) is first supplied to the preamplifier 15 to be amplified and is then supplied to the process amplifier 16 for waveform shaping and/or gamma correction. Thereafter, the signal is applied to a low-pass filter 17 and a bandpass filter 18, respectively. As a result, the luminance signal S, and a signal S =S +S,,, such as shown in FIG. 4C (or a signal S '=S ,,S, such as depicted in FIG. 4C) are respectively derived from the low-pass filter l7 and the bandpass filter 18 separately from each other. 8,, and 8,, are low frequency components or fundamental components of the chrominance signal S, and the index signal S, respectively. H

TEE 'israfib'ii oft he index signals, and the chrominance signal SC will hereinbelow be described. Since the repetitive frequencies of the index signals S, and the chrominance signal Sc are equal to each other, the separation of these signals is achieved in the following manner without using a filter.

. Reference numeral 19 indicates a delay circuit such as, for example, an ultrasonic delay line, by means of which the signal S,=S +S, (or S,=S ,,-S,,,) derived from the bandpass filter 18 is delayed by one horizontal scanning period lI-I. Reference numeral 20 designates an adder circuit and reference numeral 21, a subtraction circuit. The signals S,=S ,+S,, (or S,'=S ,,S,,,) in

a certain horizontal scanning period H, and the signal S,'=S ,;-S,,, (or S,=S ,,+S,,,) in the subsequent horizontal scanning period H which are derived from the delay circuit 19 and the bandpass filter 18 are supplied to the adder circuit 20 to be added together, providing as an outputa chrominance signal 28,-, such as depicted in FIG. 40. In this case, the content of chrominance signals in adjacent horizontal scanning periods are so similar that they can be regarded as substantially the same. Further, it is also possible to delay the signal from the bandpass filter 18 by three or five horizontal scanning periods due to their similarity.

These signals S,=S ,,+S, (or S,=S ,S, and S, =S ,,-S,,, (or S,,=S ,,+S, in the horizontal scanning periods H, and I-I, are applied to the subtraction circuit 21 to achieve a subtraction (S ,,-S,,,)(S +S,, or (S ,,+S,, )(S ,,S, to derive therefrom an index signal 2S', (or 2S',,,, though not shown) such as depicted in FIG. 4E. The resulting index signal -2S',,, (or 2S,,,) is fed to a limiter circuit 22 to render its amplitude uniform forming an index signal -2S, (or 28,) as depicted in FIG. 4F.

The index signal 2S, (or 28,) thus obtained is reversed in phase at every horizontal scanning period, so that the signal -2S, is corrected in phase in the following manner. Reference numeral 23 designates a change-over switch (an electronic switch in practice), reference numerals 23a and 23b, its fixed contacts, and reference numeral 23C, its movable contact. The output side of the limiter 22 is directly connected to one fixed contact 23a of the change-over switch 23 and to the other fixed contact 23b through an inverter 24. The change-over switch 23 is constructed such that the movable contact 230 makes contact with the fixed contacts 23a and 23b alternately for every horizontal scanning period in synchronism with the alternately signal S, impressed on the primary winding 12a of the transformer 12 to thereby derive the index signal 28, from the movable contact 230 at all times.

The chrominance signal S derived from the adder circuit 20 is supplied to synchronous detectors 25, 26, and 27, respectively. The index signal 8,, is supplied to the synchronous detector 25 through a phase shifter 28 which adjusts the phase of the index signal to the axis of the red signal in order to produce a color difference signal R-Y at the output of the detector 25. In a similar manner, the output signal from the phase shifter 28 is supplied to the synchronous detector 26 through a phase shifter 29 to produce a color difference signal G-Y at the output of the detector 26 and the output signal from the phase shifter 29 is supplied to the synchronous detector 27 through the phase shifter 30 to produce a color difference signal B-Y at the output of the detector 27. The phase shifters 29 and 30 change the phase of the input signals by respectively. These color difierence signals and the luminance signal S, are applied to a matrix circuit 31 to derive color signals S S and S,, at its terminals T T and T respectively. The color signals thus obtained may be suitably processed to produce color television signals for the NTSC system and other various systems.

It has been found that the transformer 12 in the system shown in FIG. 1 is a critical component in the satisfactory operation of the system. Leakage signals appearing at the midpoint 1,, of the secondary winding 12b may be the result of leakage from the primary winding 124. We have found that the leakage is apparently primarily caused by capacity between the primary and secondary windings and by a difference of the capacity to ground between the two sections of the secondary windings. The leakage signal present at the midpoint r, tends to produce unbalanced index signals I during each horizontal scan. As a result, the index signal tends to remain in the reproduced chrominance signal S which causes adeterioration of color fidelity. This deterioration may show up as alternate bright and dark lines in the reproduced color picture.

The ,trarisformer shown in FIGS. 6-8 is provided, in accordance with the present invention, to overcome the foregoing problems related to the transformer 12 of FIG. 1.

FIG. 7A shows a top view of a bobbin 101 and FIG. 7B shows a side view of this bobbin, which forms the first component in the construction of the transformer. The bobbin is basically a hollow tube of non-magnetic highly conductive metal, such as copper, aluminum, gold, silver, and the like, and has a center hole 101a. In order to minimize induction currents, the bobbin tube has a slot 102 that extends the entire length of the tube. Extending laterally from the tube are three flanges 103a-l03c, which are preferably of the same type of metal as the cylindrical part of the bobbin and are electrically and mechanically afflxed thereto.

The other components of the transformer are shown in FIGS. 6A and 6B. A primary winding 104, which may consist typically of four turns, is wound on the bobbin in the space between the flanges 103a and 103b. The bobbin acts as a shield for the winding but an additional metal shield of tinned ,braided copper wire 10411 is connected to the bobbin and surrounds the lead wires l04b and 1040 of the primary 104.

The secondary windings, which may consist of one turn each, are indicated by reference numerals 105 and 106 and are placed in the bobbin region between the flanges l03b and 103c. The secondary windings have terminal wires 105a and 106a, respectively, and these are twisted together outside of the transformer to equalize the capacitance to ground of this part of the transformer. The other ends of the windings 105 and 106 are also twisted together and connected to form the midpoint 107. Thus, all parts of the connections to the windings 105 and 106 are either shielded by the bobbin 101 or, where they are external to the transformer, are twisted to equalize the capacitance to ground. I

The bobbin 101 and the primary winding 104 and the secondary windings 105 and 106 are enclosed within a C-shaped conductive metal shield case 108 shown in FIGS. 8A and 8B. This shield may be of the same type of metal as that of the flanges and is both electrically and mechanically joined to the flanges to form a complete shield around the windings except for a limited slot 109, which is aligned with the slot 102 in the completed transformer. The shield case 108 also has a notch 110 at one end thereof diametrically opposite the slot 109. The depth of the notch 110 is substantially equal to the distance between the flanges 103a and 103b so that the end terminals 104b and 1040 of the primary winding 104 can be pulled through this slot to allow connections to be made. The ends 1050 and 106a and the midpoint 107 of the secondary are pulled through the slot 109 on the opposite side of the transformer. Preferably the shield case 108 is soldered to the flanges 10311-1030 and the metal shield 1040 of the primary winding 104 is soldered to the shield case 108 to form a complete shield for the transformer and its connections.

Two pot-core sections 111 and 112 fit around the transformer. These pot-cores are made of suitable ferrite material and comprise cylindrical portions closed at one end and having a hollow inner part big enough to accept the bobbin 101 and the shield case 108. At the center of each of the pot-core sections 11 l and 112 is a tions 111 and 112 are bonded to each other at their peripheral portions and at the center portion with an adhesive.

Because of the enclosed configuration of this transformer, the electric field from the primary winding 104 does not couple with the secondary windings 105 and 106 and, therefore, any leakage signal at the midpoint 107 is suppressed. This cooperates with the equalization of the capacitances to ground of the winding ends 105a and 106a of the secondary to produce a uniform index signal at every scanning line of the camera system shown in FIG. 1. One additional advantage of the potcore sections 111 and 112 is to prevent any influence from magnetic leakage flux from the outside, such as flux from the deflection yoke of the vidicon tube 1. The cores also prevent leakage flux from the transformer to the vidicon.

What is claimed is:

1. A transformer comprising:

A. A bobbin of non-magnetic conductive metal comprising:

l. a plurality of flanges, each having a generally radial slot, and

2. a hollow hub having a longitudinal slot aligned with the slots in said flanges;

B. A primary winding wound on said hub between first and second ones of said flanges;

C. A secondary winding located between said first flange and a third one of said flanges and having a center tap, said secondary winding being wound on said hub, said first one of said flanges being located between said primary and secondary windings;

D. A non-magnetic conductive metal case surrounding said bobbin and conductively connected to said flanges to suppress an electric field from said windings and having a longitudinal slot extending the length thereof and aligned with said slots in said flanges, the ends of said secondary winding being twisted together outside of said case to provide equal capacitances to ground from both ends of said secondary winding;

. A magnetic core comprising:

1. a post extending in said hollow hub, and 2. an outer portion surrounding said bobbin and non-m agnetic conductive metal case; and

. A flexible shield encircling the ends of said primary winding outside of said metal case, one end of said shield being electrically connected to said case and the other end of said braid being connected to ground.

2. The transformer of claim 1 in which said case has an additional notch diametrically opposite said slot in said case and extending into one end thereof a distance substantially equal to the distance between said first and second flanges, said ends of said primary winding extending through said notch and said ends and center tap of said secondary winding extending-through said slot in said case. 

1. a post extending in said hollow hub, and
 1. a plurality of flanges, each having a generally radial slot, and
 1. A transformer comprising: A. A bobbin of non-magnetic conductive metal comprising: 